Shear and Interface Strength of Clay at Very Low Effective Stress

Thin-specimen direct shear (TSDS) tests were conducted to measure the shearing strength of kaolinite, and interface strengths between kaolinite and acrylic plastic and anodized aluminum, at normal effective stresses from 1 to 2400 Pa (0.02 to 50 lb/ft2). At the lowest effective normal stresses, curved strength envelopes fitted through the data exhibited no cohesion and high secant friction angles. Accurate information on the behavior of soil in this low-pressure range is needed to properly interpret the behavior of prototype foundations in laboratory-scale model tests.